Dry method for separating paper constitutents for recovery and recycling

ABSTRACT

A method for separating mixtures of waste paper into two components using the differences in strength and/or waterreceptivity characteristics of the two components which are typically the liner board and corrugated medium of corrugated paper or a mixture of magazines and newsprint. In separation, the material of the paper mixture is cut into pieces ranging in size from about one to six inches in either dimension, treated with a debonding agent and then subjected to differential size reduction wherein one of the mixture components is reduced to small pieces, e.g., one-quarter inch in either dimension, while the other remains in pieces of essentially the same size. Separation of the two distinctly different sized components is then effected.

United States Patent [1 1 Iannazzi et al.

[ 1 Sept. 3, 1974 Sparrow; Richard Strauss, both of Lexington, all ofMass.

73 Assignee: Arthur D. Little, Inc., Cambridge,

Mass.

22 Filed: Sept. 27, 1972 21 Appl. No.: 292,662

[52] US. Cl. 162/5, 162/158 [51] Int. Cl. D21c 5/02 [58] Field of Search162/4, 5, 158, 8; 241/28; 209/3, 4, 9, 133, 268

[56] References Cited UNITED STATES PATENTS 1,960,106 5/1934 Grewin162/4 2,532,660 12/1950 Care 241/28 X 2,697,661 12/1954 Hollis... 162/42,776,209 l/1957 O'Flynn.... 162/5 2,912,174 11/1959 Bidwell 241/28 X2,972,171 2/1961 Heritage 241/28 X 3,216,886 ll/l965 Katzen 241/283,499,823 3/1970 Croon 162/158 FOREIGN PATENTS OR APPLICATIONS 940,250/l963 Great Britain. 162/5 OTHER PUBLICATIONS Kinne, M. R., A System forReclaiming Vinyl Coated Fiber, Tappi, Vol. 39, N0. 8, August 1956, pp.168A-l69A.

Casey, Pulp & Paper," Vol. 1, p. 373, 1960, lnterscience, New York.

Primary Examiner-S. Leon Bashore Assistant Examiner-William F. SmithAttorney, Agent, or FirmBessie A. Lepper [5 7] ABSTRACT A method forseparating mixtures of waste paper into two components using thedifferences in strength and- /or water-receptivity characteristics ofthe two components which are typically the liner board and corrugatedmedium of corrugated paper or a mixture of magazines and newsprint. Inseparation, the material of the paper mixture is cut into pieces rangingin size from about one to six inches in either dimension, treated withadebonding agent and then subjected to differential size reductionwherein one of the mixture components is reduced to small pieces, e.g.,onequarter inch in either dimension, while theother remains in pieces ofessentially the same size. Separation of the two distinctly differentsized components is then effected. i

16 Claims, No Drawings This invention relates to an essentially drymethod for separating two paper constituents and more particularly forseparating an essentially unsized, highly water-receptive paperConstituent from a sized, less waterreceptive paper constituent. Themethod may also be used to separate and remove fibrous or filmcontaminants such as asphalt-impregnated tape, plastic films and thelike. In the following description and claims the term essentially dryis used to designate paper stock having up to 35 to 40 moisture byweight.

In the recovery of paper for recyling from a composite paper productsuch as corrugated board or from a physical mixture such as acombination of newspapers and magazines, there arises the problem ofseparating two kinds of paper having different properties and physicalcharacteristics. Atleast a partial separation is essential to allow eachtype of paper to be reused in the most efficient and economical manner.

Although, as will be evident, the method of this invention is notlimited to'the processing of corrugated board, the problems which arefaced inthe industry may be illustrated with reference to the handlingof this well-known paper composite product. Corrugated board is formedas a corrugated medium between and adhered to two outside layers oflinerboard. The corrugated medium and linerboard servetwo distinct anddifferent roles and are therefore formed of two distinct and differenttypes of paper. The corrugated medium must be highly crush-resistant andhave a high degree of stiffness. It is formed of so-called semichemicalhardwood fibers which generally make up at least 80 to 85 percent of thecorrugated medium. The corrugated medium paper is as a result of itscomposition and purpose an unsized, highly water-receptive material. Inaddition, this material has comparatively low-strength characteristicswhen compared with linerboard.

In contrast to the corrugated medium, the linerboard isformed ofunbleached, softwood kraft pulp. The fibers are relatively long, thelinerboard is sized, exhibits a relatively low degree of waterreceptivity and high puncture resistance. It will be seen that if thesepaper constituents of corrugated board are recovered as a single, mixedmaterial, the recovered fibers are not ideally suitable for serving aseither corrugated medium or as linerboard since each must possessdistinct and different characteristics. Typically, a corrugated boardwill comprise some 84 pounds of linerboard per one thousand square feet,36 to 38 pounds of corrugated medium and some 6 pounds of starch usedprimarily as an adhesive.

At present there is no known commercially available, practical processfor separating the liner from the medium component in the recycle of oldcorrugated contains. An experimental method now under evaluation forseparating these two paper constituents in corrugated board involves awet process in which some by weight of hammermilled corrugated board isthoroughly mixed into about 95 by weight of water and beaten under highenergy conditions to form an allfiber slurry. Subsequent to this, thetwo types of fibers are separated by centrifuging the fiber slurry. Itwill be apparent that this requires in addition to handling a largequantity of water (which may be recycled) the processing of wet fibersto separate the two different fiber types.

As another example for the need for an efficient and economical methodfor separating paper constituents, the recovery of newsprint may becited. Newsprint itself is generally free from any sizing and is highlywater receptive. However, in the collection of old newspaper, a numberof magazines get mixed in and these are generally formed of papers whichare highly sized and coated, and which have relatively low waterreceptivity. In order to reuse the newsprint in the usual wellknownmanner to make recycled newsprint and the like it is necessary to removea substantial portion of the paper which is not newsprint. Hand sortingof the material prior to the newsprint recovery process is noteconomical and a wet process of separation is not currently available.

It will be seen from these two illustrative situations that it would bedesirable to have a method for separating two different paperconstituents which are to be reused, each for a different purpose.

It is therefore a primary object of this invention to provide animproved method for separating and recovering two different paperconstituents so that each constituent may best be used for the purposefor which it is recovered. It is another object to provide a method ofthe, character described which is an essentially dry process and whichdoes not require the separation of two types of fibers from large massesof wet fibers. It is yet another'object of this invention to provide amethod for the recovery of the two types of paper making up corrugatedboard in forms such that each type may be reprocessed and used in thesame role in reconstituted corrugated board formation as originallyused. This invention has as an additional object the providing ofchemical additives that will facilitate the differential size reductionof the component parts by weakening one component and/or strengtheningthe other component. Still an additional object is to provide a methodof the character described which enables magazine paper to beeffectivelyseparated from newsprint in the recycling of papers, Other objects ofthe invention will in part be obvious and will in part be apparenthereinafter.

By the method of this invention the corrugated board or mixture ofnewspapers and magazines is first reduced to small pieces, i.e., one toseveral square inches in area, and then chemical additives including adebonding liquid which may contain urea, ethylene carbonate, wettingagents, etc., uniformly distributed over the paper pieces. The quantityof debonding liquid is maintained at a levelwhich is no greater than 50by weight of the paper treated. Immediately or shortly after theapplication of debonding agent the paper is subjected to a differentialsize reduction treatment so that a substantial proportion of theunsized, waterreceptive constituent is reduced to fine pieces of theorder of 1/4 inch on a side while the paper constituent which is sizedand which is not readily receptive to water remains essentially in itsoriginal size, e.g., one to several square inches in area. The fractionsare .then separated out, preferably in a suitable air separator, in anessentially dry condition. In the case of corrugated board. partialdelamination to break a portion of the adhesive bond between thelinerboard and the corrugated medium is desirable, and some physicaltreatment such as dry heating may be used to enhance the debondingprocess.

The invention accordingly comprises the V several steps and the relationof one or more of such steps with respect to each of the others, and thecomposition possessing the features, properties and relation ofconstituents, which are exemplified in the following detaileddisclosure, and the scope of the invention will be indicated in theclaims.

The method of this invention may now be described in further detail. Thepaper feed, e. g., corrugated board is first reduced to small piecesseveral inches (i.e.', l to 6 inches) in either dimension. This mayconveniently be done in a shredder or in a hammermill or by a rotarycutter. if the paper is corrugated board it may in some instances bedesirable to subject these pieces to some physical treatment, such asdry heat, which will help to break the adhesive bonds between thelinerboard and the corrugated'medi um. such heating should, of course,not be performed at a temperature or for a time which would cause anyappreciable thermal degradation of any of the fibers, making up thepaper feed. This step of physical treatment is an optional one.

Where the paper feed is corrugated board, the next step is the partialdelamination of the pieces to expose at least a portion of thecorrugated medium (unsized, highly water receptivecomponent). It is notnecessary to remove all of the linerboard from the corrugated mediumandnormally about 70 delamination is sufficient. Since the. linerboardis normally adhered tothe corrugated medium by means of some suitableadhesive, elg., starch, some physicaltreatment, such as the optional dryheating step-mentioned, may be used to break the adhesivebonds beforedelamination. lf the paper feed being processed is a mixture ofnewspaper and magazines, then the delamination step, along with theoptional step of physical treatment, is eliminated.

arated materials are to be discharged in an essentially dry state it isnecessary that the amount of debonding agent which is uniformlydistributed over the milled or shredded material be controlled.Therefore, the amount of debonding liquid applied to the paper feedshould range'between about and about 50 by weight of the paper feed.Moreover, the quantity of debonding liquid used and the concentration ofthe debonding agent in the debonding liquid should be ad justed sothatfrom about 1 to about 3 by weight of debonding agentbasedonpaperfeed weight is-applied.

The liquid component of the debonding liquid serves as a lubricant aswell as a deterent to the build-up of static electricity in thesubsequent step of fiberizing in which at least a major portion, i.e.,more than 60 percent of the unsized, waterreceptive constituentisreduced to fibers. The debonding agent comprises one or morecomponents which are capable of destroying or materially reducing thehydrogen bonds in the paper constituent to be reduced to fibers.Exemplary of suitable debonding agents are urea, ethylene carbonates andsurfactants (anionic or nonionic) or mixtures of these materials. In atypical mixture the ratio of urea to ethylene carbonate may range fromabout 1 to 3 to about 3 to l, and the surfactant may be present in anamount ranging from about 0.1 to l by total weight of the urea andethylene carbonate. This debonding agent is conveniently dissolved inwater to form the debonding liquid. 1

The debonding liquid may be applied to the paper feed in any mannersuitable for attaining substantially uniform distribution of the liquidover the surfaces of the paper pieces. The spraying of the debondingliquid in the form of a fine mist into a stream of the milled paperpieces as they are discharged from the hammermill or shredder into thedifferential size reduction equipment is exemplary of one way in whichsuch uniform application may be achieved.

Once the debonding liquid is applied to the milled paper pieces, thenext step of differential size reduction follows within a short time,and preferably it follows immediately. Thus the selective size reductionshould be begun not later than about-1O minutes after application of thedebonding liquid.

In another embodiment of themethod of this invention, an additionalchemical agent may be added to the paper pieces which .willpreferentially-strengthen the less water-receptive constituent of themixture. As an example, a 2 boric acid solution may be sprayed onto thepaper pieces to gelantize the starch coating which is present on themagazine component pieces of No. l waste news. Theapplication of aneffective amount of this additive serves to increase the strength of thestarch coated paper thereby making it less susceptible to the subsequentdifferential sizing treatment.

. The controlled and selective mechanical size reduction of a'wastepaper mixture or composite material is preferably carried out in alow-energy input mill apparatus such as a Micro Bud (Trademark) mill orapparatus similar in construction and operation to a Waring blender. Thepurpose of this step of differential size reduction is to reduce a largeportion of the unsized, more water-receptive constituent into smallpieces (e.g., 1/4 inch or less) while retaining the sized, lesswater-receptive constituent in essentially its originally cut size. Thusin the case of the recovery of corrugated board,'the corrugated mediumbeing unsized and having readily absorbed the debonding liquid isreduced to small pieces while the linerboard remains substantiallyintact. In simiar fashion, the difference in water receptivity and sizecontent between newsprint and magazines is taken advantageof to reduce asubstantial portion of the newsprint to very small pieces. A minorportion of the linerboard fraction,-say between about 10- and 30 of itsoriginal weight, may be reduced-to small pieces and may be removed withthe corrugated medium fraction. However, this quantity of soft woodkraft material may be mixed with the semi-chemical hardwood of thecorrugated medium for reprocessing to form so-called bogus medium" or itmay be added to virgin semichemical pulp to make corrugated medium.

In applying the method of this invention to separating newsprint andmagazines up to about 20 of the newsprint may be removed with themagazine fraction and still provide an economical recovery system. itis, of course, preferable in all cases to carry out as complete aseparation of the constituents as is possible.

Subsequent to the step of differential size reduction, which may be acontinuous or a batch operation, the resulting mixture of small piecesof paper and those pieces which have not been appreciably reduced insize is subjected to particle classification and separation. This isconveniently done by passing the mixture through an air separator suchas a so-called Segradyne separator wherein the small lighter peices areborne out on an air stream as one fraction and the remaining largerpieces are removed as a second fraction. Both an air separator tosegregate the pieces of linerboard from the smaller pieces of corrugatedmedium. In the air separator, the corrugated medium fraction wascollected as the accepts, i.e., the lighter fraction, and the linerboardfraction was collected as the rejects," i.e., the heavier fraction.

Physical strength measurements were made on handsheets of paper formedfrom these two fractions. in forming these hand sheets the two recoveredfractions were disintegrated and dispersed in accordance with TAPPIstandard procedure No. 4 l0 for forming papermaking furnishes. The handsheets were made on a Noble-Wood laboratory apparatus from thesefurnishes and the physical data, given in Table l, were obtainedfractions after separation are essentially dry because of by standardprocedures.

Table 1 Physical Properties of Hand Sheets Fraction the relatively smallquantity of debonding liquid used. the ability to achieve effectiveseparation with a limited amount of debondingliquid is, in turn,attributable to the combination of steps used which take advantage ofthe difference in the physical and chemical characteristics of the paperconstituents being separated and recovered.

In a similar manner, paper components containing fibrous or plastic filmcontaminants such as asphalt laminated gummed tape and polyethylene filmcan be removed from the recycled product by the method of thisinvention. The stronger asphalt tape and plastic film containing pieceswill remain essentially the same size as the magazine component of amagazinenewsprint mixture feed when subjected to the differential sizereduction step. Therefore, it is possible to separate papers containingsuch contaminants along with the magazine fraction.

The method of this invention may be further described with reference tothe following example which is meant to be illustrative and notlimiting.

Samples of old corrugated boxes were cut into 1 1 inch X 1 inch squareswith a paper cutter. The squares of corrugated board were placed in aWaring blender (dry) to delaminate the linerboard and medium fractions.A l0 by weight solution of urea in water containing 0.2 by water weightof a nonionic surfactant was madeup as a debonding liquid. An amountequivalent to 40 by paper stock weight of this debonding liquidwas'applied to the delaminated pieces of corrugated board. This quantityof debonding liquid provided a urea pick-up of about 2/z%.

The pieces of board moistened with the debonding liquid were thensubjected to the action of the Waring blender for about 5-10 seconds. Asa result of this mechanical differential size reduction the corrugatedmedium was reduced to small (1/4 inch or smaller) pieces while thelinerboard fraction remained essentially intact.

This differentially sized material was then placed in From the-datagiven in Table l, which also includes the physical data on a handsheetformed of a fiber mixture recovered from corrugated board, it will beseen that an effective separation was made between the two kinds offibers used in forming the corrugated board.

This is particularly evident from the tensile and tear strength data.

In a similar'manner, magazine cover stock was mixed with newsprint andtorn into 1 inch X 1 inch pieces. The previously described solution ofdebonding agent was sprayed onto the pieces to produce about a 40moisture pick-up (2.5 urea pick-up by weight of paper). The treatedpieces were then subjected to the shearing action of the Waring Blenderfor about 5 seconds. As in the case of the corrugated board, thedifference in the physical characteristics of the two constituents madeit possible to retain most of the stronger, more water-resistantcomponent (magazine fraction) essentially intact while reducing the sizeof the more water-receptive and weaker component (newsprint fraction) toform small pieces. The two fractions were separated one from the otherby the air separation technique previously described.

The method of this invention provides an essentially dry process forseparating paper constituents which is based upon differences in waterreceptivity and physical strength. The elimination of the need to form apaper slurry elimates the need to handle wet pulp and to recycle largequantities of water.

It will thus be seen that the objects set forth above, among those madeapparent from the preceding description are efficiently attained and,since certain changes may be made in carrying out the above methodwithout departing from the scope of the invention, it is intended thatall matter contained in the above description shall be interpreted asillustrative and not in a limiting sense.

We claim:

1. An essentially dry method of separating for recovering and recyclingtwo paper constituents which differ in water receptivity, comprising thesteps of a. reducing the paper material to be separated to pieces havingmaximum dimensions no greater than six inches;

b. uniformly distributing an effective amount of a debonding liquid overthe pieces formed to selectively debond the fibers in the more waterreceptive component, said amount being no greater than about 50 by paperweight;

c. subjecting the pieces from step (b) without any additional liquid todifferential size reduction whereby the pieces of the morewater-receptive constituent are reduced to fibers and small pieces nogreater than about 1/4 inch in dimension while the major portion of theless water-receptive constituent remains essentially. intact; and

. separating out said fibers and small pieces as essentially drymaterial from said less water-receptive constituent which is also in anessentially dry condition.

2. A method in accordance with claim 1 wherein the amount of debondingliquid is equivalent to between about 20 and 50 by weight of said papermaterial.

3. A method in accordance with claim 1 wherein said debonding liquid iswater.

4. A method in accordance with claiam 1 wherein said debonding agentcomprises an aqueous solution of an active debonding'material which isurea, ethylene carbonate, or mixtures thereof, the concentration of saidactive debonding material ranging between about 2 and by weight of thewater used in forming said aqueous solution.

5. A method in accordance with claim 4 wherein said active debondingmaterial is a mixture of urea and ethylene carbonate in a weight ratioranging from about 1 to 3 to about 3 to l and said debonding liquidcontains a surfactant in an amount equivalent to form about 0.1 to l bytotal weight of said urea and ethylene carbonate.

6. A method in accordance with claim 1 wherein said two paperconstituents are the linerboard and the corrugated medium of corrugatedboard.

7. A method in accordance with claim 6 wherein said differential sizereduction is carried out until at least from about to about weightpercent of said corrugated medium is reduced to said small pieces.

8. A method in accordance with claim 6 including the step of partiallydelaminating the corrugated board subsequent to step (a) thereby toexpose said corrugated medium.

9. A method in accordance with claim 8 wherein said corrugated board issubject to physical treatment prior to said step of partiallydelaminating thereby to enhance the action of said debonding agent.

10. A method in accordance with claim 9 wherein said physical treatmentcomprises dry heating.

11. A method in accordance with claim 1 wherein said two paperconstituents are newspapers and sized magazine paper.

12. A method in accordance with claim 11 including the step of adding topieces formed in step (a) an agent I 16. A method in accordance withclaim 1 wherein said step of separating out said fibers and said smallpeices comprises carrying off said fibers and small pieces in a dry airstream.

2. A method in accordance with claim 1 wherein the amount of debondingliquid is equivalent to between about 20 and 50 % by weight of saidpaper material.
 3. A method in accordance with claim 1 wherein saiddebonding liquid is water.
 4. A method in accordance with claiam 1wherein said debonding agent comprises an aqueous solution of an activedebonding material which is urea, ethylene carbonate, or mixturesthereof, the concentration of said active debonding material rangingbetween about 2 and 10 % by weight of the water used in forming saidaqueous solution.
 5. A method in accordance with claim 4 wherein saidactive debonding material is a mixture of urea and ethylene carbonate ina weight ratio ranging from about 1 to 3 to about 3 to 1 and saiddebonding liquid contains a surfactant in an amount equivalent to formabout 0.1 to 1 % by total weight of said urea and ethylene carbonate. 6.A method in accordance with claim 1 wherein said two paper constituentsare the linerboard and the corrugated medium of corrugated board.
 7. AmethoD in accordance with claim 6 wherein said differential sizereduction is carried out until at least from about 70 to about 90 weightpercent of said corrugated medium is reduced to said small pieces.
 8. Amethod in accordance with claim 6 including the step of partiallydelaminating the corrugated board subsequent to step (a) thereby toexpose said corrugated medium.
 9. A method in accordance with claim 8wherein said corrugated board is subject to physical treatment prior tosaid step of partially delaminating thereby to enhance the action ofsaid debonding agent.
 10. A method in accordance with claim 9 whereinsaid physical treatment comprises dry heating.
 11. A method inaccordance with claim 1 wherein said two paper constituents arenewspapers and sized magazine paper.
 12. A method in accordance withclaim 11 including the step of adding to pieces formed in step (a) anagent capable of gelatinizing the sizing on said magazine paper therebyto render it even less water receptive.
 13. A method in accordance withclaim 1 wherein at least a portion of said less water-receptiveconstituent comprises contaminants such as asphalt-gummed tape, plasticfilms and the like.
 14. A method in accordance with claim 1 wherein nolonger than 10 minutes elapses between the performance of step (b) andstep (c).
 15. A method in accordance with claim 1 wherein said step ofsubjecting said pieces to differential size reduction is carried out ina low-energy level input mill.
 16. A method in accordance with claim 1wherein said step of separating out said fibers and said small peicescomprises carrying off said fibers and small pieces in a dry air stream.